Abstract

An isolated colorless spot of 1° diameter located at the antisolar point was observed from a plane on the clouds beneath it. The spot can be explained by light scattering on randomly oriented ice crystals via light paths similar to those responsible for the subparhelic circle. Its peculiar polarization properties potentially permit its detection in cases where the spot is embedded in a glory.

© 2008 Optical Society of America

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References

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  1. M. Bodó, “2008. Légköroptikai jelenségek,” http://cygni.multiply.com/photos/album/25.
  2. W. Tape, Atmospheric Halos, Vol. 64 of the Antarctic Research Series (American Geophysical Union, 1994).
  3. L. Cowley, “Antisolar Region Arcs,” http://www.atoptics.co.uk/halo/antisol.htm.
  4. F. de Comité, “Subhorizon diffuse arcs with Liljequist subparhelia,” 14 August 2006, http://haloreports.blogspot.com/2006/08/subhorizon-diffuse-arcs-with.html.
  5. P. Laven, “Atmospheric glories: simulations and observations,” Appl. Opt. 44, 5667-5674 (2005).
    [CrossRef]
  6. L. Cowley and M. Schroeder, “HaloSim3 Software,” http://www.atoptics.co.uk/halo/halfeat.htm.
  7. G. P. Können, Polarized Light in Nature (Cambridge U. Press, 1985).
    [CrossRef]
  8. C. Hinz and G. P. Können, “Unusual glories,” Weather 63 (2008), in press. doi: 10.1002/wea.311.
    [CrossRef]
  9. G. P. Können, “Identification of odd-radius halo arcs and of 44°/46° parhelia by their inner-edge polarization,” Appl. Opt. 37, 1450-1456 (1998).

2008

C. Hinz and G. P. Können, “Unusual glories,” Weather 63 (2008), in press. doi: 10.1002/wea.311.
[CrossRef]

2005

1998

Bodó, M.

M. Bodó, “2008. Légköroptikai jelenségek,” http://cygni.multiply.com/photos/album/25.

Cowley, L.

L. Cowley and M. Schroeder, “HaloSim3 Software,” http://www.atoptics.co.uk/halo/halfeat.htm.

L. Cowley, “Antisolar Region Arcs,” http://www.atoptics.co.uk/halo/antisol.htm.

de Comité, F.

F. de Comité, “Subhorizon diffuse arcs with Liljequist subparhelia,” 14 August 2006, http://haloreports.blogspot.com/2006/08/subhorizon-diffuse-arcs-with.html.

Hinz, C.

C. Hinz and G. P. Können, “Unusual glories,” Weather 63 (2008), in press. doi: 10.1002/wea.311.
[CrossRef]

Können, G. P.

C. Hinz and G. P. Können, “Unusual glories,” Weather 63 (2008), in press. doi: 10.1002/wea.311.
[CrossRef]

G. P. Können, “Identification of odd-radius halo arcs and of 44°/46° parhelia by their inner-edge polarization,” Appl. Opt. 37, 1450-1456 (1998).

G. P. Können, Polarized Light in Nature (Cambridge U. Press, 1985).
[CrossRef]

Laven, P.

Schroeder, M.

L. Cowley and M. Schroeder, “HaloSim3 Software,” http://www.atoptics.co.uk/halo/halfeat.htm.

Tape, W.

W. Tape, Atmospheric Halos, Vol. 64 of the Antarctic Research Series (American Geophysical Union, 1994).

Appl. Opt.

Weather

C. Hinz and G. P. Können, “Unusual glories,” Weather 63 (2008), in press. doi: 10.1002/wea.311.
[CrossRef]

Other

M. Bodó, “2008. Légköroptikai jelenségek,” http://cygni.multiply.com/photos/album/25.

W. Tape, Atmospheric Halos, Vol. 64 of the Antarctic Research Series (American Geophysical Union, 1994).

L. Cowley, “Antisolar Region Arcs,” http://www.atoptics.co.uk/halo/antisol.htm.

F. de Comité, “Subhorizon diffuse arcs with Liljequist subparhelia,” 14 August 2006, http://haloreports.blogspot.com/2006/08/subhorizon-diffuse-arcs-with.html.

L. Cowley and M. Schroeder, “HaloSim3 Software,” http://www.atoptics.co.uk/halo/halfeat.htm.

G. P. Können, Polarized Light in Nature (Cambridge U. Press, 1985).
[CrossRef]

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Figures (3)

Fig. 1
Fig. 1

Bright spot at the antisolar point. Its diameter is 1 ° . The contrast is enhanced by unsharp masking. The picture was taken while flying over Serbia, between Belgrade and Szeged. Solar elevation was 12.5 ° . The horizontal field of view is 52 ° . (Photographed by Mónika Bodó on a flight from Athens to Budapest on 27 March 2008, 15:45 UTC).

Fig. 2
Fig. 2

If this ice crystal is in plate orientation, that is with its C axis vertical, the light path depicted here creates the subparhelic circle, which is a horizontal circle below the horizon passing through the antisolar point. If the crystals are randomly oriented, the light path creates a spot-shaped intensity enhancement at the antisolar point.

Fig. 3
Fig. 3

Simulation of the light distribution in the antisolar region due to light scattering by randomly oriented hexagonal ice crystals with aspect ratio ( c / a ) = 1 . The spot in the center of the picture appears exactly at the antisolar point; its diameter is 0.7 ° . The horizontal field of view of the figure is 18 ° . The simulation is made with the HaloSim program authored by L. Cowley and M. Schroeder [6]; the 0.5 ° diameter of the solar disk is taken into account.

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